System and method for forming aluminum fuse for compatibility with copper BEOL interconnect scheme

ABSTRACT

A semiconductor fuse device and a method of fabricating the fuse device including a last metal interconnect layer including at least two discrete metal conductors, an inter-level dielectric layer deposited over the last metal interconnect layer and the at least two discrete metal conductors, a thin wire aluminum fuse connecting the at least two discrete metal conductors, and a fuse opening above the aluminum fuse.

BACKGROUND

1. Field of the Invention

The embodiments presented herein generally relate to the design andfabrication of a semiconductor fuse that is compatible with copper metalBack-End-Of-Line (BEOL) processing for use in a radiation hardenedStatic Random-Access Memory (SRAM). More particularly, the embodimentsincorporate an aluminum fuse into the environment of a metal (e.g.,copper) interconnect level.

2. Description of Related Art

For radiation hardened semiconductor fabrication applications, e-fusesand copper fuses are incompatible with application conditions. Aradiation hardened circuit cannot reliably un-bias a copper fuse as itmay normally be un-biased for other copper BEOL processes. Additionally,e-fuse technology is also incompatible with radiation hardenedarchitecture.

Due to an inability to un-bias a copper fuse, and concern for copperfilament formation in a radiation hardened design environment, analternative material, structure and method of fabrication is necessaryto overcome these limitations in the radiation hardened SRAMenvironment.

An alternative aluminum composition fuse is presented herein thatovercomes these limitations.

SUMMARY OF THE INVENTION

According to one example, a semiconductor fuse device includes a metalinterconnect layer including at least two discrete metal conductors,where an inter-level dielectric layer is deposited over the metalinterconnect layer and the at least two discrete metal conductors. Aconductive fuse connects the at least two discrete metal conductors, anda fuse opening above the conductive fuse is positioned between the atleast two discrete metal conductors.

According to another example, a semiconductor fuse device includes anuppermost metal interconnect layer including a plurality of metalconductors, where an inter-level dielectric layer is deposited over theuppermost metal interconnect layer and at least two discrete metalconductors. A conductive fuse connects at least two discrete metalconductors in the uppermost metal interconnect layer by a central linearfuse portion, and a fuse opening is positioned above the central linearfuse portion.

According to another example, a method of fabricating a semiconductorfuse includes forming a metal interconnect layer including at least twodiscrete metal conductors, where an inter-level dielectric layer isprovided above the metal interconnect layer and the at least twodiscrete metal conductors. A conductive fuse is deposited into a portionof the inter-level dielectric layer and is electrically connectedbetween the at least two discrete metal conductors. A portion of theinter-level dielectric layer is removed above the conductive fuse tocreate a fuse opening.

According to another example, a method of fabricating a semiconductorfuse includes forming an uppermost metal interconnect layer including aplurality of metal conductors, and forming an inter-level dielectriclayer above the uppermost metal interconnect layer and at least twodiscrete metal conductors. A conductive fuse is deposited into a portionof the inter-level dielectric layer and is electrically connected to theat least two discrete metal conductors with a central linear fuseportion. A portion of the inter-level dielectric layer is removed abovethe central linear fuse portion to create a fuse opening.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other exemplary purposes, aspects and advantages willbe better understood from the following detailed description of anexemplary embodiment herein with reference to the drawings, in which:

FIG. 1 is a schematic diagram of a sectional view of fabricating a fusein a semiconductor;

FIG. 2 is a schematic diagram of another sectional view of fabricating afuse in a semiconductor according to FIG. 1;

FIG. 3 is a schematic diagram of a first embodiment illustrating asectional view of an aluminum fuse in a semiconductor;

FIG. 4 is a schematic diagram of a second embodiment illustrating asectional view of another aluminum fuse in a semiconductor;

FIG. 5 is a schematic diagram of a third embodiment illustrating asectional view of yet another aluminum fuse in a semiconductor; and

FIG. 6 is a logic flowchart for an embodiment for a method offabricating an aluminum fuse in a semiconductor.

DETAILED DESCRIPTION

Referring now to the drawings, and more particularly to FIGS. 1 and 2,there are shown exemplary illustrations of the method and structures ofa fuse embedded in a semiconductor.

For purposes herein, a “semiconductor” is a material or structure thatmay include an implanted impurity that allows the material to sometimesbe a conductor and sometimes be an insulator, based on electron and holecarrier concentration. As used herein, “implantation processes” can takeany appropriate form (whether now known or developed in the future) andcan comprise, for example, ion implantation, etc.

FIG. 1 illustrates a schematic diagram of a sectional view offabricating a fuse in a semiconductor device 2.

An uppermost or last metal interconnect layer 10 of a semiconductordevice 2 includes a dielectric layer 12 that includes metalinterconnection structures, such as metal conductors 14A, 14B and 14C,which may comprise copper. The last metal interconnect layer is boundedby a lower cap layer 16 and an upper cap layer 18. The upper cap layer18 may be a copper diffusion barrier. A final insulator layer 20 isdeposited on top of the upper cap layer 18 of the last metalinterconnect layer 10. A mask is applied (not shown) to the finalinsulator layer 20 to remove material in the final insulator layer 20such that conductive portions, in particular, conductive pad 22A andfuse, indicated generally as 22B are deposited through the finalinsulator layer 20 to contact an upper portion of the metal conductors14A, 14B and 14C, respectively in the last metal interconnect layer 10.

For purposes herein, an “insulator” is a relative term that means amaterial or structure that allows substantially less (<95%) electricalcurrent to flow than does a “conductor.” The dielectrics (insulators)mentioned herein can, for example, be formed by plasma deposition ofSiO2 or SiO2 based materials by reacting either tetra-ethyl-ortho-silane(TEOS) or silane with O2 or activated O2, i.e. O3 or O⁻. Alternatively,the dielectrics herein may be formed from any of the many candidate highdielectric constant (high-k) materials, including but not limited tosilicon nitride, silicon oxynitride, a gate dielectric stack of SiO2 andSi3N4, and metal oxides like tantalum oxide. The thickness ofdielectrics herein may vary contingent upon the required deviceperformance.

The conductors mentioned herein can be formed of any conductivematerial, such as polycrystalline silicon (polysilicon), amorphoussilicon, a combination of amorphous silicon and polysilicon, andpolysilicon-germanium, rendered conductive by the presence of a suitabledopant. Alternatively, the conductors herein may be one or more metals,such as tungsten, hafnium, tantalum, molybdenum, titanium, nickel,aluminum, or copper, or a metal silicide, any alloys of such metals, andmay be deposited using physical vapor deposition, chemical vapordeposition, or any other technique known in the art.

An oxide layer 24 covers the conductive pad 22A and fuse 22B and theremaining exposed portions of the final insulator layer 20. FIG. 1illustrates a mask 26 patterned and applied to the top surface of theoxide layer 24 where an initial pad channel opening 28 is formed in theoxide layer 24 using a material removal process.

A hardmask can be formed of any suitable material, whether now known ordeveloped in the future, such as a metal or organic or inorganic (Si3N4,SiC, SiO2C (diamond)) hardmask, that has etch resistance greater thanthe substrate and insulator materials used in the remainder of thestructure.

When patterning any material herein, the material to be patterned can begrown or deposited in any known manner and a patterning layer (such asan organic photoresist) can be formed over the material. The patterninglayer (resist) can be exposed to some pattern of light radiation (e.g.,patterned exposure, laser exposure, etc.) provided in a light exposurepattern, and then the resist is developed using a chemical agent. Thisprocess changes the physical characteristics of the portion of theresist that was exposed to the light. Then one portion of the resist canbe rinsed off, leaving the other portion of the resist to protect thematerial to be patterned. A material removal process is then performed(e.g., plasma etching, etc.) to remove the unprotected portions of thematerial to be patterned. The resist is subsequently removed to leavethe underlying material patterned according to the light exposurepattern.

FIG. 2 shows a schematic diagram illustrating another sectional view offabricating a fuse in a semiconductor where the mask 26 of FIG. 1 isremoved and an imageable polyimide layer 30 is used to define openingsover both the conductive pad 22A and the fuse 22B. A pad opening 32 iscreated over a portion of the conductive pad 22A using a through viaprocess (RIE) to reduce over-etching over the conductive pad 22A. Aportion of the conductive pad 22A is completely exposed through the padopening 32. Additionally, a fuse opening 34 is created in the polyimidelayer 30 via a material removal process (RIE) using a selective maskingprocess. When the fuse opening 34 is created, a thin passivation layerremains over the linear fuse portion 22C.

In the device shown in FIGS. 1 and 2, the fuse 22B may be constructed ofa variety of materials, including tungsten, hafnium, tantalum,molybdenum, titanium, nickel, aluminum, or copper, as is known in theart. Typically, the linear fuse portion 22C is a few millimeters thick.However, in a radiation hardened application, it is desirable for thefuse to be much thinner; for example, having a thickness less than 4microns to as thin as less than 1 micron.

FIG. 3 illustrates a schematic diagram of a first embodiment,constructed in a manner similar to the process shown in FIGS. 1 and 2.FIG. 3 shows a sectional view of an aluminum fuse, indicated generallyas 102, in a semiconductor device 100 where the aluminum fuse 102 has apair of vertical via portions 103 and 104 that extend from the metalconductors 14B and 14C through the upper cap layer 18 and finalinsulator layer 20 into the oxide layer 24. A linear fuse portion 106extends between the metal conductors 14B and 14C and is locatedcompletely within the final insulator layer 20, contacting the lowestportion of the final insulator layer 20 and proximate the upper surfaceof the last metal interconnect layer 10 on the top of the upper caplayer 18. Thus, in this embodiment, when viewed in cross-section asshown in FIG. 4, the fuse structure includes a linear fuse portion 106connected between two inverted U-shaped vertical via portions 103, 104that contact the metal conductors 14B, 14C. The U-shaped vertical viaportions 103, 104 pass through the final insulator layer 20 and into theoxide layer 24 before contacting the linear fuse portion 106 from abovethe linear fuse portion 106. The vertical via portions 103 and 104 maybe a few millimeters thick such as fuse 22B as shown in FIGS. 1 and 2;however, the linear fuse portion 106 is much thinner; for example,having a thickness less than 4 microns to as thin as less than 0.25microns.

In this embodiment, a fuse opening 108 extends through the polyamidelayer 30, the oxide layer 24, and into the final insulator layer 20stopping just above the upper surface of the linear fuse portion 106such that there is a small amount of final insulator layer 20 betweenthe linear fuse portion 106 and the fuse opening 108.

FIG. 4 illustrates a schematic diagram of a second embodiment,constructed in a manner similar to FIGS. 1 and 2. FIG. 4 shows asectional view of another aluminum fuse, indicated generally as 202, ina semiconductor device 200 where the aluminum fuse 202 extends from thetop surface of the metal conductors 14B and 14C only into the finalinsulator layer 20 such that the linear fuse portion 204 contacts thelowest portion of the final insulator layer 20 and is proximate theupper surface of the last metal interconnect layer 10 on the top of theupper cap layer 18. The end portions 205 and 206 that contact the metalconductors 14B and 14C may be a few millimeters thick such as fuse 22Bas shown in FIGS. 1 and 2; however, the linear fuse portion 204 is muchthinner; for example, having a thickness less than 4 microns to as thinas less than 0.25 microns.

In this second embodiment, a fuse opening 208 extends through thepolyamide layer 30, the oxide layer 24, and into the final insulatorlayer 20 stopping just above the upper surface of the aluminum fuse 202such that there is a small amount of final insulator layer 20 betweenthe linear fuse portion 204 and the fuse opening 208.

FIG. 5 illustrates a schematic diagram of a third embodiment,constructed in a manner similar to FIGS. 1 and 2. FIG. 5 shows asectional view of yet another fuse 302 in a semiconductor device 300where the fuse 302 extends from the top surface of the metal conductors14B and 14C entirely within the upper cap layer 18. The upper cap lay 18may be a copper diffusion barrier and the fuse 302 may comprise arefractory metal, such as tantalum or tantalum nitride. In thisembodiment, the metal conductors 14B and 14C contact the fuse 302 frombelow the fuse 302, which is a thin wire; for example, having athickness less than 4 microns to as thin as less than 0.25 microns.

In this third embodiment, a fuse opening 308 extends through thepolyamide layer 30, the oxide layer 24, and into the final insulatorlayer 20 stopping just above the upper surface of the fuse, indicatedgenerally as 302, such that there is a small amount of final insulatorlayer 20 between the fuse 302 and the fuse opening 308.

In summary, the semiconductor fuse device includes a last metalinterconnect layer 10 including at least two discrete metal conductors14B and 14C, an inter-level dielectric layer, 20, 24 and/or 30 depositedover the last metal interconnect layer 10, and the at least two discretemetal conductors 14B and 14C, an aluminum fuse 102, 202, or 302connecting the at least two discrete metal conductors 14B and 14C, and afuse opening 108, 208, or 308 above the aluminum fuse 102, 202, or 302,respectively, and positioned between the at least two discrete metalconductors 14B and 14C.

In a first embodiment, the semiconductor fuse device includes theinter-level dielectric layer comprising the final insulator layer 20proximate the last metal interconnect layer 10, the oxide layer 24, andpolyimide layer 30 on the final insulator layer 20, the aluminum fuse102 comprising a linear fuse portion 106 contacting a lowermost portionof the final insulator layer 20, where the remainder of the linear fuseportion 106 is positioned entirely within the final insulator layer 20.The aluminum fuse 102 has U-shaped vertical via portions 103 and 104that connect to the two discrete metal conductors 14B and 14C throughthe final insulator layer 20 and the oxide layer 24 and polyimide layer30. The fuse opening 108 projects through the final insulator layer 20and the oxide layer 24 and polyimide layer 30.

In a second embodiment, the semiconductor fuse device includes theinter-level dielectric layer comprising the final insulator layer 20proximate the last metal interconnect layer 10, the oxide layer 24, andpolyimide layer 30 on the final insulator layer 20, the aluminum fuse202 comprising a linear fuse portion 204 contacting a lowermost portionof the final insulator layer 20, where the remainder of the linear fuseportion 204 is positioned within the final insulator layer 20. Thealuminum fuse 202 connects the two discrete metal conductors 14B and 14Conly through the final insulator layer 20. The fuse opening 208 projectsthrough the oxide layer 24 and polyimide layer 30 and the finalinsulator layer 20.

In a third embodiment, the semiconductor fuse device includes theinter-level dielectric layer comprising the final insulator layer 20proximate the last metal interconnect layer 10 having an upper cap layer18, an oxide layer 24 and a polyimide layer 30 on the final insulatorlayer 20, the fuse 302 comprising a thin metal wire. The fuse 302connects the two discrete metal conductors 14B and 14C entirely withinthe upper cap layer 18. The fuse opening 308 projects through the oxidelayer 24 and polyimide layer 30 and the final insulator layer 20.

The last metal interconnect layer 10 may include metal conductors 14Band 14C, and the fuse opening may be positioned above a portion of thefinal insulator layer 20 above the aluminum fuse 102, 202, or 302. Themetal conductors 14B and 14C may comprise copper conductor structures.

FIG. 6 illustrates a logic flowchart for an embodiment for a method offabricating an aluminum fuse in a semiconductor including providing anuppermost metal interconnect layer including a plurality of metalconductors 600. An inter-level dielectric layer is provided above theuppermost metal interconnect layer 602. An aluminum fuse is depositedinto a portion of the inter-level dielectric layer and electricallyconnected to at least two discrete metal conductors with a thin centrallinear fuse portion 604. A portion of the inter-level dielectric layeris removed above the central linear fuse portion to create a fuseopening 606.

In a first embodiment, the method of fabricating a semiconductor fuseincludes providing a final insulator layer proximate the uppermost metalinterconnect layer and oxide and nitride layers on the final insulatorlayer. Depositing the aluminum fuse further includes forming U-shapedvertical via pairs and a central linear fuse portion that contacts alowermost portion of the final insulator layer, where the remainder ofthe central linear fuse portion is positioned entirely within the finalinsulator layer. The fuse opening projects through the oxide and thenitride layers into the final insulator layer.

In a second embodiment, the method of fabricating a semiconductor fuseincludes providing a final insulator layer proximate the uppermost metalinterconnect layer and oxide and nitride layers on the final insulatorlayer. Depositing the aluminum fuse further includes forming a centrallinear fuse portion contacting a lowermost portion of the finalinsulator layer, where the remainder of the central linear fuse portionis positioned within the final insulator layer. The connection betweenthe aluminum fuse and the discrete metal conductors is formed onlythrough the final insulator layer in this embodiment. The fuse openingprojects through the oxide and nitride layers into the final insulatorlayer.

In a third embodiment, the method of fabricating a semiconductor fuseincludes providing a final insulator layer proximate the uppermost metalinterconnect layer and oxide and nitride layers on the final insulatorlayer. Depositing the fuse further includes forming a linear fuseportion entirely within the upper cap layer. The connection between thefuse and the discrete metal conductors is formed directly in thisembodiment; the entire fuse is below the final insulator layer. The fuseopening projects through the oxide and nitride layers into the finalinsulator layer.

The method of fabricating a semiconductor fuse may further includeforming copper conductor structures in the last or uppermost conductorlayer. The fuse opening may further be positioned above a portion of anoxide layer on the aluminum fuse. The fuse opening may further includecontemporaneously removing a second portion of the inter-leveldielectric layer above another metal conductor in the uppermost metalinterconnect layer to create a bond opening to another metal conductor.

Embodiments described herein teach methods for forming an aluminum fusein a copper interconnect scheme. Aluminum metallurgy is not susceptibleto filament formation under biasing, in the same manner that a copperfuse might be. While aluminum is disclosed as a fuse material in theseveral embodiments described herein, other appropriate conductivematerials for use in a radiation hardened environment, such as tantalumor tantalum nitride, may be used.

With its unique and novel features, the embodiments herein may providean aluminum fuse for connection to the last metal connect layer of asemiconductor device that enables the un-biasing of the aluminum fuse,and forms a proper fuse filament in a radiation hardened designenvironment.

In addition, terms such as “right”, “left”, “vertical”, “horizontal”,“top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”,“over”, “overlying”, “parallel”, “perpendicular”, etc., used herein areunderstood to be relative locations as they are oriented and illustratedin the drawings (unless otherwise indicated). Terms such as “touching”,“on”, “in direct contact”, “abutting”, “directly adjacent to”, etc.,mean that at least one element physically contacts another element(without other elements separating the described elements).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of this disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescriptions of the various embodiments of the present invention havebeen presented for purposes of illustration, but are not intended to beexhaustive or limited to the embodiments disclosed. Many modificationsand variations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

The invention claimed is:
 1. A semiconductor device comprising: a metalinterconnect layer including at least two discrete metal conductors; aninter-level dielectric layer positioned adjacent said metal interconnectlayer, said inter-level dielectric layer comprising a first layer havinga first thickness and at least one other layer having a secondthickness; a conductive fuse positioned within said inter-leveldielectric layer, said conductive fuse having a first end and a secondend, said conductive fuse being directly connected on said first end andsaid second end to said metal conductors, said conductive fuse furthercomprising: a first U-shaped vertical via on said first end and a secondU-shaped vertical via on said second end, and a thin linear fuse portionextending between said first U-shaped vertical via on said first end andsaid second U-shaped vertical via on said second end, said thin linearfuse portion being a sacrificial portion of said fuse, each of saidfirst U-shaped vertical via and said second U-shaped vertical viaextending from the end directly connected to said metal conductorthrough said first layer and at least partially into said at least oneother layer, and said linear fuse portion being positioned completelywithin said first layer, and said linear fuse portion directlycontacting a lowest portion of said first layer; and a fuse recessformed partially through said inter-level dielectric layer, said fuserecess extending completely through said at least one other layer andinto said first layer, said fuse recess being positioned adjacent saidlinear fuse portion, a thickness of said inter-level dielectric layerbetween said linear fuse portion and said fuse recess being less thansaid first thickness.
 2. The semiconductor device according to claim 1,a thickness of said linear fuse portion being less than 1 micron.
 3. Thesemiconductor device according to claim 1, further comprising at leastone additional insulator layer positioned adjacent said inter-leveldielectric layer, said fuse recess extending through said additionalinsulator layer to an exterior of said semiconductor device.
 4. Thesemiconductor device according to claim 1, each of said first end andsaid second end of said conductive fuse extending into said metalinterconnect layer to connect to said metal conductors.
 5. Thesemiconductor device according to claim 1, said metal conductorscomprising copper and said conductive fuse comprising tantalum nitride.6. The semiconductor device according to claim 1, said conductive fusecomprising aluminum.